In vitro and in vivo treatment of cancer cells and treatment of viruses with a tripeptide compound

ABSTRACT

The cancericidal activity of all the permutations of a tripeptide compound formed from dichlorodiethylaminophenylalanine, parafluorophenylalanine and methionine bonded together with peptide links was demonstrated using seven in vitro tumor cell lines. The viabilities of each of the tumor cell lines were significantly reduced by treatment for 1 to 24 hours with 1 to 50 ug of the tripeptide per ml of carrier solvent. A pulse exposure to the tripeptide demonstrated that the reductions in tumor cell was comparable to continuous exposure. Other in vitro tests were all conducted on AKR mice. Methods of treating virus by exposing the virus to one of the noted tripeptide compounds is also contemplated. Methods of treating tumor cells with the tripeptides dissolved in a solvent consisting of dimethylacetamide, propylene glycol and absolute ethanol are also contemplated by the present invention. Methods of treating tumor cells resistant to other chemotherapeutic agents is contemplated by this invention.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 654,477 filed Sept. 26, 1984, now abandoned, which is a continuation-in-part of copending application U.S. Ser. No. 621,796, filed June 18, 1984 now U.S. Pat. No. 4,540,683; which is a continuation-in-part of copending U.S. Ser. No. 468,036, filed Feb. 23, 1983 now U.S. Pat. No. 4,508,710, which is a continuation-in-part of U.S. application Ser. No. 455,477, filed Jan. 4, 1983, now abandoned; which is a continuation-in-part of U.S. application Ser. No. 311,646, filed Oct. 15, 1981, now U.S. Pat. No. 4,428,875, which is a continuation-in-part of U.S. application Ser. No. 173,621, filed July 30, 1980, now U.S. Pat. No. 4,314,999; which is a continuation-in-part of application Ser. No. 929,237, filed July 31, 1978, now U.S. Pat. No. 4,216,208.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of treating different types of cancer cells either in vitro or in vivo by treatment with a tripeptide in which the amino acid dichlorodiethylaminophenylalanine is bonded by peptide links to parafluorophenylalanine and methionine.

2. Prior Art

Chemotherapy has been and still is an object of intense research. Certain positive results have undoubtedly been achieved, especially by means of polychemotherapy realized by associating different active substances according to carefully developed protocols. However, the ideal therapy has not been found. The need to find new active substances has been particularly emphasized. All the foregoing justifies continuous research directed toward preparing new chemotherapeutic compounds active against cancerous tumors. There are already known peptides having anti-tumor activity, consisting of both normal and antimetabolic amino acids, coupled by means of a peptide bond. Such peptides have for years been in therapeutic use with favorable results both in monochemotherapy and in polychemotherapy.

As disclosed in copending U.S. application Ser. No. 311,646, a new family of antitumor compounds is characterized in that each compound comprises the amino acids dichlorodiethylaminophenylalanine, parafluorophenylalanine and methionine bonded together by CO--NH peptide links formed by the respective amino and carboxyl groups of the said amino acids. All possible permutations of the three amino acids are set forth as follows:

1. pFPne. MPhe. Met

2. pFPhe. Met. MPhe

3. MPhe. pFPhe. Met

4. MPhe. Met. p.FPhe

5. Met. pFPhe. MPhe

6. Met. MPhe. p.FPhe

wherein "MPhe" indicates the amino acid dichlorodiethylaminophenylalanine having the structural formula: ##STR1## and wherein "pFPhe" indicates the amino acid parafluorophenylalanine having the structural formula: ##STR2## and wherein "Met" indicates the amino acid methionine having the structural formula: ##STR3## The above-identified tripeptides are useful in the treatment of malignant tumors. The above noted tripeptides are prepared by condensing one of the amino acids having a blocked amine group with another of said amino acids having a blocked carboxyl group with the aid of dicyclohexylcarbodiimide; removing one of the blocking groups to form a dipeptide having a blocked amine or carboxyl group; and condensing the dipeptide with the third amino acid to form the tripeptide with the aid of dicyclohexylcarbodiimide. Compounds of the tripeptide can also be formed, such as compound, by esterifying the tripeptide; and introducing hydrogenchloride.

To further illustrate the synthesis of a tripeptide compound, the following specific process is set forth.

CHEMICAL SYNTHESIS Synthesis of 3-(p-fluorophenyl)-L-alanyl-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanine ethyl ester. Depeptide I by Reaction I ##STR4##

To m-bis(2-chloroethyl)aminophenyl-L-alanine ethyl ester [25.88 g] in 150 ml of tetrahydrofuran [15.37 g°], 3-(p-fluorophenyl)-L-alanine [17.18 g] and of N,N-dicyclohexylcarbodiimide (coupling agent) [15.85 g] were added successively while stirring for 15 minutes at 0° C. Temperature was then allowed to rise to 20° C. and the reaction mixture was held at this conditionn for 5 hours. At the completion of the reaction, dicyclohexylurea was removed by filtration and the filtrate was evaporated at 40° C. at a reduced pressure. Residue then was recovered by adding ethyl ether (150 ml) and the precipitate was recovered by filtration, and vacuum dried at 40° C. The raw substance was further purified by crystallization in 96% ethyl alcohol yielding a white crystalline substance (Dipeptide I) with MP 126°-7° C. Analysis showed a molecular composition of C₂₅ H₃₀ FCl₂ N₃ O₄ (M=526.44). The calculated molecular composition of the substance in %: C 57.04-H 5.74-N 7.98-Cl 13.47; and found %: C 56.88-H 5.71-N 8.01-Cl 13.32. The overall yield of the reaction was 73% Dipeptide I.

Synthesis of 3-(p-fluorophenyl)-L-alanyl]-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanine. Dipeptide II by Reaction II ##STR5##

The white crystalline substance [26.3 g] (Dipeptide I) from Reaction I was dissolved in acetone [130 ml] by gently heating at 40° C. After cooling it to room temperature, 50 ml of 1N NaOH was added while stirring for 1 hour at 20° C. The hydrolysis reaction was monitored with TLC using a mixture of ethyl alcohol/ethyl acetate/acetic acid: 50:50:1 (v/v/v) solvent system. At the completion of reaction, 50 ml of 1N HCl were slowly added. The white precipitate (Dipeptide II) thus formed was separated by filtration and washed with water until disappearance of Cl from the filtrate. The thus obtained substance was first air dried then vacuum dried. The white amorphous substance had the following characteristics: MP 203°-206° C., a molecular composition of C₂₃ H₂₆ FCl₂ N₃ O₄ (M=498.39). The calculated composition in %: C 55.43-H 5.26-N 8.43-Cl 14.23, found %: C 55.17-H 5.24-N 8.47-Cl 14.81. The yield of Reaction II was 95% of Dipeptide II.

Synthesis of 3-(p-fluorophenyl)-L-alanyl-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanyl-L-methionine ethyl ester. Tripeptide III by Reaction III ##STR6##

Dipeptide II (27.7 g) derived from reaction II was dissolved in 225 ml of N,N-dimethylformamide at 40° C. After cooling it to 15° C., a solution of L-methionine ethyl ester [10.28 g] in 20 ml of N,N-dimethylformamide was added, followed by successive addition of N-hydroxysuccinimide [8.6 g] and N,N-dicyclohexylcarbodiimide [12.57 g] in 25 ml of N,N-dimethylformamide. The thus obtained mixture was held at 5° C. for 30 minutes while stirring. Then the temperature was allowed to rise to 20° C. Dicyclohexylurea was removed by filtration, and to the filtrate while stirring, 1800 ml of water was added at 15° C. After washing, the filtrate was air dried and then successively kept under vacuum in the presence of P₂ O at 40° C. Purification of the crude substance was achieved by suspending it in 120 ml of absolute ethyl alcohol and solubilized by adding small portions of N,N-dimethylformamide and suspended for 15 hours at 5° C. The crystalline product was filtered and washed with absolute ethyl alcohol and dried under vacuum at 40° C. The white crystalline substance, Tripeptide III had the following properties: MP 187°-189° C., an analysis showing C₃₀ H₃₉ FCl₂ N₄ O₅ S (M=657.64), with--calculated composition (%) C 54.79-H 5.98-N 8.51-Cl 10.78-S 4.87. Found (%): C 54.03-N 5.89-N 8.52-Cl 10.71-S 4.84.

Synthesis of 3-(p-fluorophenyl)-L-alanyl-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanyl-L-methionine ethyl ester HCl. Tripeptide IV compound by Reaction IV ##STR7##

Tripeptide III [17.75 g] from Reaction III was suspended in 250 ml HCl solution (4.1% w/v) in absolute ethyl alcohol and was stirred for 4 hours at 20° C. The reaction mixture was held for 15 hours at 5° C. The course of hydrolysis reaction was monitored with TLC using ethyl ester/acetic acid/water=135:27:9 (v/v/v) solvent system. At the completion of the reaction, to the resulting clear solution 250 ml of water were slowly added while stirring and maintaining the pH at 3-3.2 with NaHCO₃ at 5° C. After 20 minutes agitation, the white bulky substance with filtered followed by washing with cold water at 5° C. The sample was first air dried, then vacuum dried at 40° C. in the presence of P₂ O₅. Purification of the crude product was performed. Crystallization in isopropyl alcohol at 60°-65° C. was conducted after which the product in the isopropyl alcohol was cooled for 16 hours, at 15° C., filtered, washed first with isopropyl alcohol, then with acetone and dried under vacuum at 40° C. for 8 hours. The analysis of the resulting white crystalline substance (the tripeptide compound) showed the following characteristics MP 180°-182° C.; Analysis: for C₂₉ H₃₉ Cl₂ FN₄ O₄ S HCl (MW=666.08); Calculated %: C 52.29-H 6.05-N 8.41-Cl 15.97-S 4.81; Found %: C 52.31-H 6.09-H 8.38-Cl 15.85-S 4.76.

SUMMARY OF THE INVENTION

All six of the specific tripeptide compounds have similar characteristics and results in treating malignant tumor cells as well as viruses. For the purposes of simplification, only the tripeptide compounds set forth previously in the chemical synthesis, is employed with regard to the remaining disclosure.

In order to investigate the chemotherapeutic effect of the tripeptide compound, various in vitro and in vivo analyses utilizing a variety of different origins and etiologies, as well as, primary human ALL, AMML and Hairy cell leukemias.

In order to determine the length of exposure to the tripeptide compound necessary to induce cytopathology and cytolysis, tumor cells were treated for periods ranging from 15 minutes to several hours.

The in vitro analysis of the cytolytic potential of the tripeptide compound was carried out using well characterized rodent, primate, and human tumor cell models. The first series of experiments investigated the dosage and the length of exposure to the tripeptide compound necessary to induce irreversible cytopathology or morphological alterations of the neoplastic cells. The viabilities of each of the seven in vitro tumor cells tested was significantly reduced by the treatment from 1 to 24 hours, with 1 to 50 ug of the tripeptide compound per ml of solvent carrier. Under identical treatment conditions, freshly isolated human leukemic cells, particularly all lymphoblast cells, were more susceptible to the tripeptide compound than any of the other tumor models. Prolonged exposure of the tumor cells to the tripeptide compound increased the rate of tumor cell death.

In view of the broad spectrum of in vitro therapeutic activity of the tripeptide compound against tumor cells, a study was initiated to determine the in vivo therapeutic activity. There is considerable evidence that leukemia in AKR mice mimics human leukemias in many respects, and it is probable that AKR mice leukemia is analogous to human acute T-cell lymphocytic leukemia.

Tumor bearing mice were treated with a single dose of 10, 15, or 20 mg of the tripeptide compound per kg of rodent weight. The results clearly demonstrate that the tripeptide compound effectively reduced the tumor burden with an increase in the mean survival time (MST) from 8 to 30 days and the "cure" of 30% of the treated mice. It is also important and significant that the tripeptide compound provide good sustainment of remission as indicated by the fact that 30% of the treated animals were alive 80 days after treatment.

The following description will more fully describe the chemotherapeutic effect of the tripeptide compound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows survival of L-1210 leukemia suspensions following a 30 min (A) or 1 hr (B) pulse exposure to 1 (Δ...Δ), 5( - ), 10 ( -- ) and 25 ( - ) ug of the tripeptide/ml of carrier solvent. L-1210 cell suspensions contained 6×10⁵ cells/ml at the time of treatment and the range of viable control cells during the 5-day observation period was 6.5-10×10⁵ cells/ml.

FIG. 2 shows survival of B-16 melanoma cell layers following 30 min (A) or 1 hr (B) pulse treatment with 5 ( -.- ), 10 ( -- ), 25 ( - ), and 50 (X--X) ug of the tripeptide ml of carrier solvent. The numbers of cells in the 24-hr-old layers at the time of treatment were 2.7-3×10⁵ B-16 melanoma cells per well. The ranges of viable control cell numbers during the 15-day observation period were 3.5-12×10⁵ MJY-alpha cells and 1.5-4×10⁵ B-16 cells per well.

FIG. 3 shows survival of MJY-alpha mammary tumor cells following 30 min (A) or 1 hr (B) pulse treatment with 5 ( -.- ), 10 ( -- ), 25 ( - ) and 50 (X--X) ug of the tripeptide/ml of carrier solvent. The numbers of cells in the 24-hr-old layers at the time of treatment were 2.9-3.2×10⁵ MJY-alpha cells. The ranges of viable control cell numbers during the 5-day observation period were 3.5-12×10⁵ MJY-alpha cells.

FIG. 4 shows DBA/2 mice inoculated intraperitoneally with 10⁶ L-1210 leukemia cells on Day 0. (A) Control animals. Mice were treated on Day 2 with the tripeptide at (B) 10 mg/kg of rodent weight; (C) 15 mg/kg; and (D) 20 mg/kg.

FIG. 5 shows change of organ weights after chemotherapy with the tripeptide treated AKR mice with spontaneous leukemia. Chemotherapy consisted of: Group A: 10 mg/kg of rodent weight on days 1 and 14; Group B: 5 mg/kg on days 1, 4, 7, 21, and 42. At designated intervals 4 mice from each experimental group were selected at random, sacrificed and their spleen and thymus weights determined. Group A: Mean thymus wt (Δ--Δ); Mean spleen wt (□--□) Group B: Mean thymus wt ( -- ); Mean spleen wt ( -- ).

FIG. 6 shows AKR mice with spontaneous leukemia. Control mice ( ); mice received intraperitoneal injections of the tripeptide at 10 mg/kg on days 1 and 14 (Therapy A; ), and 5 mg/kg on days 1, 4, 6, 21, and 42 (Therapy B; ).

FIG. 7 shows in vivo tumorigenicity of L-1210 leukemia, MJY-alpha mammary tumor, and B-16 melanoma treated with 1 to 50 ug of the tripeptide/ml. Tumor cells were treated for 15 min to 4 hr, washed and grafted into syngeneic hosts at a concentration of 1×10⁶.

FIG. 8 shows average tumor size of MJY-alph mammary tumor cells or B-16 melanoma implanted into BALB/c and C57BL/6 mice, respectively as a function of time after implantation. Tumor cells were treated for 2 hrs with 0 ( -- ), 5 (x--x), 10 ( -- ), 25 (Δ--Δ), and 50 (□--□) ug of tripeptide/ml, washed and grafted at 10⁶ cells s.c. The readings are averages obtained from 2 experiments with a total of 25 to 40 animals per group.

FIG. 9 shows survival of L-1210 leukemia cells following 15, 30 and 60 min treatment with 1 ( -- ), 5 (x--x), 10 ( -- ), 25 (Δ--Δ) ug of tripeptide/ml. L-1210 cell suspensions contained 1×10⁶ cells at the time of treatment. Viability was determined for 7 days and the data represent the average of duplicate samples from 2 experiments.

FIG. 10 shows survival of MJY-alpha mammary tumor cells following 30, 60 and 120 min exposure to the tripeptide concentrations of 5 (x--x), 10 ( -- ), 25 (Δ--Δ), and 50 ( -- ) ug/ml (5 ug/ml at 30 minutes not shown). Cells were treated at 1×10⁶ cells/ml and were then seeded at 2×10⁵ cells/2 2 cm² following washing. Viability was monitored daily for 7 days. The data represent the average of duplicate samples from 3 experiments.

FIG. 11 shows survival of B-16 melanoma cells following 60, 120 and 240 min exposure to 5 (x--x), 10 ( -- ), 25 (Δ--Δ), and 50 ( -- ) ug of tripeptide/ml. B-16 cells were treated at a concentration of 6×10⁵, washed, seeded at 2.2×10⁵ cells/2 cm² and viability determined for 7 days. Data represent the average of duplicate samples from 3 experiments.

FIG. 12 shows the result of eight (8) different treatments of MJY-alpha mammary tumor cell layers after incubation. The photomicrographs were at 340 powers of magnification, except for photographs c and d which were at 670 powers of magnification. The tumor cells were treated as follows: a. With diluent only for 60 minutes, incubated one (1) day; b. With diluent only for 60 minutes, incubated for (4) days; c. With 25 ug PTT.119 for 15 minutes, no incubation--immediately after exposure; d. With 25 ug PTT.119 for 60 minutes, no incubation--immediately after exposure; e. With 10 ug PTT.119 for 60 minutes, one (1) day incubation; f. With 10 ug PTT.119 for 60 minutes, two (2) days incubation; g. With 10 ug PTT.119 for 60 minutes, four (4) days incubation; h. With 10 ug PTT.119 for 60 minutes seven (7) days incubation.

FIG. 13 shows four (4) thin sections of MJY-alpha mammary tumor cells with magnification at 45,000× through an electron microscope. Photograph A shows budding and mature B-type virus particles both in the main photograph and in the insert, for untreated cells. Photograph B shows untreated cells with aggregates of intracytoplasmic A-type virus particles and also numerous microvilli with budding particles. Photograph C shows cells treated with 25 ug PTT.119/ml for 2 hours, washed, and then incubated for one (1) day before processing for electron microscopy. Although there are some microvilli with budding particles present, the number is reduced from Photographs A and B. Photograph D shows cells treated and washed in the same way as in C, but allowed to incubate 2 days before being porcessed for electron microscopy. The number of microvilli to be observed are decreased from the number of Photographs A and B.

FIG. 14 shows the percent of tumor cell survival related to the number of days following treatment of L1210, L1210 L-pAM and P388/L-PAM leukemia suspensions following exposure to 7.5 uM PTT.119 for 30 ( -- ) or 60 ( -- ) min, or L-PAM for 30 ( -- ) or 60 (Δ--Δ) minutes. Viability data are the means of 20 evalutations with standard deviations of less than 10%, and are representative of values obtained from 2 to 4 other experiments.

FIG. 15 shows the percent of tumor cell survival related to the number of days following treatment of L-1210, L1210/L-PAM and P388/L-PAM leukemia suspensions following exposure to 15 uM PTT.119 for 30 ( -- ) or 60 ( -- ) minutes, or L-PAM for 30 ( -- ) or 60 (Δ--Δ) minutes. Viability data are the means of 20 evaluations with standard deviations of less than 10%, and are representative of values obtained from 2 to 4 other experiments.

FIG. 16 shows in vivo tumorigenicity of L1210 and L1210/L-PAM leukemia treated with 7.5 or 15 uM PTT.119 (solid bar) or L-PAM (striped bar). Tumor cells were treated for 15, 30 or 60 minutes, washed and 1×10⁶ cells injected i.p. into BDF₁ hosts. Number of tumor free mice were determined 45 days after implantation. Values represent averages of two experiments each containing groups of 10 to 15 mice.

FIG. 17 shows the percent of tumor cell survival related to drug concentration (uM) of L1210, L1210/L-PAM, and P388/L-PAM leukemia suspensions following 24 hour exposure to PTT.119 ( -- ) or L-PAM ( -- ). Data are the means of 30 to 40 evaluations obtained from three experiments.

FIG. 18 shows the percent of tumor cell survival related to PTT.119 concentration (uM) of L1210S ( -- ), L1210DDP ( -- ), and L1210 MTX ( -- ) leukemia cell lines following 24 hour exposure to PTT.119. Data are the means of three experiments carried out in duplicate.

DETAILED DESCRIPTION OF THE EMBODIMENTS In Vitro Preparation

The preparation for the in vitro analysis of the tumor cells is as follows: The murine mammary tumor cell line, MJY-alpha, was derived from adenocarcinomas induced in BALB/cfC3H females as a result of infection and oncogenesis by the mouse mammary tumor virus (MMTV). The epithelioid cell line was tumorigenic in syngenic BALB/c hosts and was used between the 25th and 65th in vitro subcultures. Growth medium was RPMI medium No. 1640 supplemented with 18% fetal calf serum, 10 uM bovine insulin, penicillin (250 U/ml) and streptomycin (100 ug/ml).

B-16 melanoma cell cultures were established from the transplantable B-16 tumor line passaged subcutaneously in male, C57BL/6Jx mice. Melanomas from 3 to 5 mice were finely minced, washed three times with serum-free growth medium and cultured as explants using Minimal Essential Medium containing D-valine and Earle's compounds supplemented with 20% calf serum and antibiotics. Confluent primary explant cultures were subsequently passaged weekly as single cell suspensions using a solution of STV. Two, 4 to 12 month old B-16 cell culture initiated in this manner were used between their 13th to 45th in vitro passages. Both in vitro lines of B-16 cells contained melanized cells and were tumorigenic in syngenic mice.

Primary L-1210 leukemia suspension cultures were initiated from the virulent, in vivo ascites line maintained in DBA/2 Ba mice or their F₁ hybrid, BDF₁ (BALB/c×DBA/2). L-1210 cells were harvested by washing the peritoneal cavity of tumor-bearing mice with physiological saline (0.85% NaCl, pH 7.2) containing 5% heparin (v/v) without preservatives. Leukemic cells were separated on Ficoll-Hypaque gradients followed by several washes in 0.01M phosphate-buffered saline, pH 7.4. Tumor cell preparations were consistently free of erythrocytes, and 98% of the L-1210 cell population excluded trypan blue. Suspension cultures were initiated and maintained in RPMI medium No. 1630 containing 10% fetal calf serum and antibiotics.

The Epstein Barr Virus infected human, B-lymphoma cell lines; Raji and P₃ HR-1 were cultured as suspensions in RPMI medium No. 1640 supplemented with 10% heat inactivated fetal calf serum, penicillin (250 U/ml) and streptomycin (250 ug/ml). Culture densities were adjusted to 5-10×10⁵ cells/ml and media replenished twice a week.

The 5-78 T cell rabbit (AACR strain) lymphoma, and the EBV-infected B lymphoma B95-8 from marmosets were also maintained as suspension cultures. Their growth conditions were similar to that used for culture of the human lymphoma cell lines.

Human AMML, ALL and Hairy cell leukemia were obtained from untreated patients undergoing leukophoresis prior to chemotherapy. Leukemic cells were separated on Ficoll-Hypaque gradients and processed as outlined for L-1210 cells.

All cultures were incubated at 37° C. in a humidified atmosphere of 5% CO₂ in air. Media, culture fluids and cell suspension were routinely checked for bacterial and fungal contaminations by use of tryptose phosphate broth; cultures were also checked for mycoplasma contamination by the method of Todaro et al.

PREPARATION OF THE CHEMOTHERAPEUTIC AGENT

The tripeptide compound 3-(p-fluorophenyl)-L-alanyl-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanyl-L-methionine ethyl ester hydrochloride) was initially dissolved at a concentration of 10 mg per ml of a solution of 0.25 ml of N,N-dimethylacetamide, 0.25 ml of absolute ethanol and 0.5 ml of propylene glycol. In the solvent solution, the absolute ethanol can be replaced with Tween 80 or other physiological and pharmaceutical emulsifiers. Stock solutions of one or two mg per ml were prepared by further dilution in an aqueous solution of 50% propylene glycol just prior to use. Aliquots of all stock solutions were added directly to the culture media to obtain a final concentration of 0.1-50 mg/ml. Controlled cultures treated with diluent received the identical volume of stock solution without the chemotherapeutic agent.

TREATMENT OF MJY-ALPHA AND B-16 CELL LAYERS

MJY-alpha mammary tumor cell layers were initiated at 2×10⁵ cells/2 cm² well (Nuncion Multidish 4, Vangard International, Neptune, NJ) using cells spontaneously released into the medium from confluent 6-8 day old cell layers. B-16 melanoma cells obtained from 4-day-old cell confluent cultures by trypsinization with STV were plated at 2.2×10⁵ cells/cm² well. These seeding densities yielded lightly confluent layers (2.3-2.6×10⁵ cells/cm²) within 24 hr. One day after subculture, the cell layers were rinsed with media and then treated with either media with no additives, or media containing the tripeptide, at concentrations ranging from 1 to 50 ug/ml media. Treatment periods ranged from 15 min to 24 hr at 37° C. Following treatment the layers were rinsed twice and reincubated with growth media: media were changed daily until the cultures were terminated.

TREATMENT OF LYMPHOID CELL LINES AND HUMAN LEUKEMIAS

All rabbit, marmoset and human lymphoid in vitro cell lines, murine L-1210 leukemia and primary human leukemias were treated at cell concentrations of 6-10×10⁵ cells/ml. The tripeptide was added to the cell suspensions to yield final concentrations of 1 to 50 ug/ml. Cultures were treated at 37° C. for periods ranging between 15 min to 24 hr. Following treatment, aliquots were removed and centrifuged at 800 rpm for 9 min, at 5° C. Treatment media were gently aspirated and the lymphoid cells resuspended in fresh growth media and reincubated at 37° C. Culture media were changed daily by gently pelleting the cells and exchanging 60-70% of the spent supernatant with fresh media.

TUMOR CELL SURVIVAL

Survival of tumor cell layers or suspensions was ascertained using 0.5% trypan blue in 0.1M phosphate-buffered saline, pH 7.25. Cell layers were released from the Multidish-4 wells with 0.5 ml STV, diluted 2 to 10 fold with the vital strain; tumor cells in suspension cultures were directly mixed 1:1 with the trypan blue dye. Tumor cells were enumerated using a haemocytometer; all 10 fields were counted for every sample. Percent viable cells was determined by direct comparison of the numbers of cells excluding trypan blue in treated cultures to those in untreated or diluent-treated parallel cultures. There were no significant differences in the viability of cells treated with diluent when compared to untreated cells.

EXPERIMENTAL EXAMPLE 1

The ability of the tripeptide compound to inhibit the growth and survival of neoplastic cells was first assessed using the MJY-alpha mammary tumor cell line and the transplantable L-1210 leukemia. The numbers of viable cells in the vitro MJY-alpha cell layers and L-1210 cell suspensions were determined following continuous 24 hr. exposure to 0.1 to 50 ug of the tripeptide compound per ml. Significant decreases in mammary tumor (46-80%) and leukemia cells (18-94%) survival were observed at all concentrations of the tripeptide compound tested including dosages less than 10 ug/ml (Table 1). The results reveal that the cancericidal activity of the tripeptide compound resulted from the direct interaction of the drug with the tumor cells and that it did not require metabolic conversion by the animal hosts for activation.

                  TABLE 1                                                          ______________________________________                                         CYTOTOXIC EFFICACY OF THE TRIPEPTIDE                                           COMPOUND AND PARENTAL COMPONENTS                                               L-1210 leukemia cell suspensions (1 × 10.sup.6 cells/ml) and             MJY-alpha mammary tumor cell layers (2.5 × 10.sup.5                      cells/cm.sup.2)                                                                were treated for 24 hr and the percentage of viable cells                      compared to untreated cells and control cells receiving diluent.               Percent Tumor Cell Survival                                                    L-1210 Leukemia  MJY-Alpha Mammary Tumor                                       ug of Tripeptide compound/ml                                                                    ug of Tripeptide compound/ml                                  0.1  1      5      10   25   1    5    10   25   50                            ______________________________________                                         82   70     62     28   6    54   41   36   27   20                            ______________________________________                                    

EXPERIMENTAL EXAMPLE 2

In order to establish the in vitro spectrum of the cancericidal activity of the tripeptide compound against various cell types, leukemias of B and T cell origins, melanoma and mammary tumor cell lines were subjected to continuous tripeptide compound treatment. Loss of cellular viability was observed in all tumor cell lines following 24 hr exposure to the tripeptide compound (Table 2). Decreases in tumor cell survival were observed at all doses, and the sensitivity of each tumor cell line was dose dependent between the concentrations of 1 to 50 ug of tripeptide compound/ml. Comparison of the leukemia, melanoma, and mammary cancer cell types revealed that they were differentially susceptible to the tripeptide compound induced cytotoxicity at any given concentration of the tripeptide compound. Leukemia cells were usually more susceptible to the cancericidal action of the tripeptide compound and cellular toxicity was observed within the first 4 hrs of exposure. However, appreciable decreases in mammary tumor and melanoma cell survivals were detected only after 8 hrs of treatment with the tripeptide compound.

The tripeptide treatment of the murine mammary tumor cell lines, MJY-alpha, not only reduced tumor cell survival in a dose-dependent manner but also decreased the production of extra cellular mouse mammary tumor virus (MMTV). Replication of this B-type retrovirus was reduced by 27% when MJY-alpha cells were exposed to 10 microgram of the tripeptide/ml for zero to 24 hours; continuous treatment for another 24 hours further reduced MMTV production by 82%. These decreases could not be accounted for by the degree of the tripeptide induced sytolysis; tumor cell survival was reduced by only 8% and 25%, respectively, during these time periods.

In order to unravel the antimetabolic activity of the tripeptide, we carried out several experiments to ascertain the effects of the compound on viral replication. Our previously described studies assessing the cancericidal activity of the tripeptide in nine tumor cell lines (Table 2) indicated that in addition to the increased sensitivity of lymphoma-leukemia cells to the agent, cells infected with and producing RNA or DNA viruses were generally more sensitive. Examination of the cellular metabolism using radio-labeled nucleic and amino acids demonstrated that the antiviral activity was not the result of blockage in cellular uptake and incorporation of precursors.

Utilizing isotopically-labeled uridine, a significant decrease was detected in the production of the RNA tumor virus MMTV by the MJY-alpha mammary tumor cells. Viral replication was reduced by 42% when cells were treated with 10 ug of the tripeptide at the time labeling. Cultures treated with this concentration 24 hours following radiolabeling of the cells also produced 37% less MMTV compared to controls, indicating that antiviral activity was not merely the result of a cellular blockage in the uptake of precursors.

The structural proteins on MMTV virions purified from cultures treated with the tripeptide were analyzed in order to determine if the tripeptide induced any biochemical changes in the particles. Profiles of MMTV glycol proteins and non-glycosylated polypeptides obtained by sodium dodecyl-sulfate polyacrylamide gel electrophoresis revealed a specific 60 to 78% decrease in the major non-glycosylated core protein, P24. The relative levels of the other MMTV polypeptides were not affected.

                                      TABLE 2                                      __________________________________________________________________________     Tumor cell layers and suspensions were exposed to 1 to 50 ug                   of the tripeptide salt per ml for 24 hr. Viability was determined              after 1, 4, 8 and 24 hr. of treatment. Results are the                         average of duplicate samples of at least three separate experiments.                                     % tumor cell                                                      Virus    Tri-                                                                               survival                                             Cell  Cell        Pro-                                                                               peptide                                                                            exposure (hr)                                        Line  Type   Type duction                                                                            ug/ml                                                                              1   4   8  24                                        __________________________________________________________________________     Mouse                                                                          L-1210                                                                               Leukemia                                                                              MuLV +   1   95  ND  100                                                                               65                                                              5   100 84  ND 57                                                              10  92  75  ND 12                                                              25  50  25  15 0                                         B-16  Melanoma                                                                              --   -   5   100 100 100                                                                               74                                                              10  100 100 63 64                                                              25  100 100 92 60                                                              50  100 100 58 33                                        MJY-alpha                                                                            Mammary                                                                               MMTV ++  5   100 100 100                                                                               53                                              Tumor           10  100 100 100                                                                               53                                                              25  100 100 98 25                                                              50  98  87  62 19                                        Rabbit                                                                         5-78  T-lymphoma                                                                            HVA  +   5   100 88  ND 66                                                              10  89  61  ND 49                                                              25  75  32  14 6                                                               50  57  4   ND 2                                         Marmorset                                                                      B-95-8                                                                               B-lymphoma                                                                            EBV  +   10  100 100 ND 40                                                              25  100 86  49 20                                                              50  77  42  26 6                                         Human                                                                          Raji  B-lymphoma                                                                            EBV  -   10  98  98  ND 82                                                              25  100 97  97 35                                                              50  94  90  76 20                                        P HR-1                                                                               B-lymphoma                                                                            EBV  +   10  96  91  ND 75                                                              25  92  86  ND 69                                                              50  93  75  ND 60                                        __________________________________________________________________________      .sup.1 MuLV = murine leukemia virus; MMTV = mouse mamary tumor virus; HVA      = herpesvirus ateles; EBV = EpsteinBarr virus.                                 .sup.2 ND = Not Done.                                                    

EXPERIMENTAL EXAMPLE 3

Leukemic cells obtained by leukophoresis from untreated patients with Hairy cell, AMML, and ALL leukemias were continuously treated with the tripeptide compound (Table 3). Lymphoblast from a patient with ALL leukemia were particularly sensitive to the tripeptide compound; cell survival was reduced by 75% following treatment with as low as 1 ug of the tripeptide compound. AMML and Hairy cell leukemias were also sensitive to all concentrations of the tripeptide compound; the numbers of viable cells were reduced by 34% to 96% after 24 hr treatment. It is noteworthy that cytotoxicity was detected in the fresh leukemia preparations within the first hour of the tripeptide compound treatment; the surviving fractions ranged from 0 to 100% in a dose dependent manner. Similar levels of cell death were never immediately observed in any of the tumor cell models at these concentrations. The cancericidal activity of the tripeptide compound was also greater against uncultured human tumor cells than any of the tumor cell lines after 24 hrs of treatment.

                  TABLE 3                                                          ______________________________________                                         EFFICACY OF THE                                                                TRIPEPTIDE SALT AGAINST HUMAN CELLS                                            Human leukemic cells obtained by leukophoresis from untreated                  patients were treated with 1 to 50 ug of the tripeptide salt for               24 hr. Tumor cell viability was determined on duplicate samples                following 1, 4, and 24 hr. exposure.                                                     Concentration                                                                             % Tumor cell survival                                               Tripeptide Exposure (hr)                                                       (ug/ml)    1       4       24                                        ______________________________________                                         Hairy cell leukemia                                                                        5            100     80    34                                                  10           100     71    81                                                  25           92      71    12                                                  50           37      21    7                                       AMML        1            95      85    66                                                  5            50      52    66                                                  10           60      41    21                                                  25           20      15    14                                                  50           4       3     4                                       ALL (N cell 1            98      76    25                                      leukemia)   5            46      29    7                                                   10           32      15    0                                                   25           15      15    0                                                   50           0       0     0                                       ______________________________________                                    

EXPERIMENTAL EXAMPLE 4

Several of the tumor cell models and the primary human leukemias displayed tripeptide compound induced cytotoxicity within 1 to 4 hours of exposure to the tripeptide compound indicating that continuous 24 hr treatment may not be required for the reduction of the tumor cell populations. To delineate the minimum concentrations and duration of the tripeptide compound exposure to induce cytolysis, MJY-alpha and B-16 melanoma cell layers and L-1210 leukemia cell suspensions were exposed to 0.5 to 50 ug of the tripeptide compound per ml of solvent for 0.25 to 4 hours. The tripeptide compound was then removed and the cells washed and reincubated in media growth. Tumor cell viability was determined 24 hrs after pulse tripeptide compound exposure. Cell survival of all three tumor cell lines was reduced by an exposure period of as short as 15 min (Table 4). The degree of cytolysis increased with extension of the treatment periods from 15 min to 4 hrs, although the decreases in cell survival were not proportional to the duration of the exposure. However, a concentration dependent decrease in cell survival was observed in the three murine tumor models for each treatment period. Comparison of the data in Tables 2 and 4 reveal that cells exposed to the tripeptide compound for one hour were irreversibly damaged when assayed a day later despite their apparent viability immediately after treatment. Of greater importance was the demonstration that pulse exposure to any concentration of the tripeptide compound was almost as effective as continuous 24 hr treatment in reducing the number of tumor cells.

                  TABLE 4                                                          ______________________________________                                         SUSCEPTIBILITY OF TUMOR CELL TO PULSE-                                         TREATMENT WITH THE TRIPEPTIDE SALT                                             MJY-alpha mammary tumor and B-16 melanoma cell layers and                      L-1210 leukemia cell suspensions were pulse-treated with the                   tripeptide salt, washed with media and their viability determined              24 hr. later. Values are the average of duplicate samples                      from four experiments.                                                                        Percent Tumor Cell Survival                                                    Treatment Period (hr)                                           Cell Line  Tripeptide                                                                               .25     .5   1    2    4                                  ______________________________________                                         MJY-alpha  5         .sup. ND.sup.1                                                                         94   89   77   76                                            10        68      67   70   64   48                                            25        61      37   51   46   44                                            50        45      32   41   ND   ND                                 B-16 Melanoma                                                                             5         ND      93   88   66   79                                            10        ND      75   68   73   63                                            25        82      67   60   56   52                                            50        65      62   48   ND   ND                                 L-1210 Leukemia                                                                           .5        95      90   83   94   68                                            1         80      87   83   78   45                                            5         72      60   61   57   35                                            10        53      40   27   31   37                                            25        20       7    0    0    0                                            20         0       0    0   ND   ND                                 ______________________________________                                           .sup.1 ND = Not Done.                                                   

EXPERIMENTAL EXAMPLE 5

Pulse treatment of mammary, melanoma and leukemia tumor cells with the tripeptide compound reduced the number of viable cells 24 hrs after exposure. In order to ascertain if the remaining cells were resistant to the tripeptide compound and be able to replicate and repopulate the culture vessels, longitudinal assessments of the surviving cell fractions were made. MJY-alpha mammary tumor and B-16 melanoma cell layers, and L-1210 leukemia cell suspensions were treated with 1 to 50 ug of the tripeptide compound per ml for 30 min or 1 hr. Cell viabilities were determined over 5 days (FIGS. 1-3). In all three tumor systems, cell viabilities decreased over the examination period indicating that the population was irreversibly affected by pulse exposure to tripeptide compound. The degree and rates of tumor cell susceptibility were dependent on the tumor cell system, as well as, on the concentration and duration of the tripeptide compound exposure. Of the three tumor models, the L-1210 leukemia was the most susceptible; at any given concentration of the tripeptide compound, approximately 5 times more L-1210 cells were destroyed compared to mammary tumor and melanoma cells.

Unlike either the L-1210 leukemia and B-16 melanoma cultures which showed a gradual progression of cell cytotoxicity with increasing dosages, there was a distinct separation of cell viability between 10 and 25 ug/ml in MJY-alpha mammary tumor cells (FIG. 3). Whether this reflected a critical threshold level of the tripeptide compound for this cell line or demarcated two populations of susceptible cells is not known. In all three tumor systems, extension of the treatment period from 0.5 to 1 hour usually resulted in a more rapid rate of cell death during the first 2 to 3 days following exposure, but did not necessarily effect the total numbers of viable cells remaining on days 4 and 5. It is also significant that the cancericidal activity of the tripeptide compound was more pronounced against fresh, human ALL, AMML and Hairy cell leukemias than established tumor cell lines of murine, rabbit, primate and human origins.

IN VIVO PREPARATION EXPERIMENTAL EXAMPLE 6

In view of the broad spectrum of in vitro therapeutic activity of the tripeptide compound against murine, rabbit, primate, and human tumor cell lines, an experiment was initiated to determine the in vivo therapeutic activity of the tripeptide compound. The following experiments were performed with the tripeptide compound. Male mice were inoculated intraperitoneally on day 0 with 10⁶ untreated leukemia L-1210 cells. The tumor bearing mice were treated 48 hours later with a single dose of 10, 15, and 20 mg of the tripeptide compound per kg weight of the test animal. Results clearly demonstrate the tripeptide compound effectively reduced the tumor burden with an increase of the mean survival time from 8 to 30 days (275%) and the apparent "cure" of the 30% of the treated animals. See FIG. 4.

EXPERIMENTAL EXAMPLE 7

Leukemia in AKR mice, which is the result of the oncogenic activity of the endogenous Gross leukemia virus, has been effectively used as a model for human leukemias in the studies of tumor biology, chemotherapy, and chemoimmunotherapy. There is considerable evidence that leukemia in the AKR mice mimics human leukemias in many respects, and it is probable that AKR leukemia is analogous to human acute T-cell lymphocytic leukemia. Leukemic cells first appear in the thymus of mice at 6 to 12 months of age. Controlling this disease is formidable, since the cure or long range control of spontaneous leukemia in AKR mice require the therapeutic eradication of virtually all of the oncogenic cells. The time lapse between the first appearance of viable lymphoma cells in the thymus and the clinical diagnosis is about 30 days.

The effectiveness of the tripeptide compound in the treatment of spontaneous leukemia in AKR mice was tested. The clinical diagnosis of spontaneous leukemia in AKR mice was made with 95% accuracy by splenic and lymph node palpation, followed by leukocyte count. There is good evidence that at the time of clinical diagnosis there are 0.6-1.8×10⁹ widely disseminated lymphoma cells in AKR mice. Without cytoreductive therapy, AKR mice die after diagnosis of spontaneous leukemia at the rate of 50% by 14 days, 90% by 33 days, and 96% by 56 days. In the preliminary experiment using AKR mice with spontaneous leukemia, good remission induction was achieved with the tripeptide compound administered either at 10 mg per kg weight of test animal on days 1 and 14, or at 5 mg of the tripeptide compound per kg of the test animal on days 1, 4, 7, 21, and 42. Significant reductions in leukemic thymus and spleen weights were observed after chemotherapy (FIG. 5). Reduction of thymus and spleen weights to normal is indicative of eradication of the primary tumor. Leukemic AKR mice receiving either treatment sustained a mean survival time of 200% and 100%, respectively. It is also important and significant that the tripeptide compound treatment provides good sustainment since 30% of the treated animals in either group were alive after the onset on the therapy (FIG. 6).

EXPERIMENTAL EXAMPLE 8

Data presented in FIG. 7 shows that L-1210 leukemia cells were the most susceptible to the cancericidal activity of the tripeptide. Concentrations as low as 5 and 10 ug tripeptide/ml effectively abrogated the leukemogenicity of the L-1210 cells. No tumor growth was apparent in the recipient mice receiving L-1210 cells treated with 5 ug for 2 hr, or 10 ug for 30 min or longer. The synthetic tripeptide effectively reduced the population of L-1210 cells capable of proliferation to 0. To ascertain if the recipients' immune responses were elicited against the tripeptide-treated leukemia cells, BDf₁ mice which had survived unsuccessful grafts of tripeptide-treated L-1210 leukemia cells for 45 days were challenged with a second graft of 1000 untreated L-1210 cells. There were no differences in the leukemogenesis of the L-1210 cells in these recipients and all mice like the controls died of tumor on days 12 and 13 demonstrating that implantation of L-1210 cells treated with tripeptide did not confer protection on the hosts to future grafts.

Loss of tumorigenicity of MJY-alpha mammary tumor and B-16 melanoma tumor cells was also apparent following tripeptide treatment (FIG. 7). In both tumor systems complete absence of tumor growth was observed in recipients of 10⁶ cells treated with tripeptide concentration of 25 ug or higher for 30 to 240 min. Exposure to the tripeptide compound reduced the viable population of MJY-alpha and B-16 tumor cells by at least 99.9% since their LD₁₀₀ doses are 100 viable cells. At lower tripeptide dosages, complete elimination of L-1210 leukemia, MJY-alpha mammary tumor and B-16 melanoma tumorigenicity were unattainable and significant extensions of the mean survival time (MST) of the recipient mice were observed (Table 5). BDf₁ mice receiving L-1210 leukemia cells treated with 5 ug of the tripeptide compound for 30 or 60 min had an ILS (increased life span) of 110% and 220%, respectively. Similarly, the survival of BALB/c mice implanted with 10⁶ MJY-alpha mammary tumor cells or C57BL/6 mice receiving B-16 melanoma cells treated with 5 to 25 ug tripeptide/ml were extended significantly beyond the 42 or 28 days, respectively, observed in the control hosts.

                  TABLE 5                                                          ______________________________________                                         MEAN SURVIVAL TIME (MST) OF SYNGENEIC Recipients                               OF TRIPEPTIDE TREATED TUMOR CELLS                                              Tumor cells were treated with the tripeptide compound in vitro,                washed and implanted subcultaneously into syngeneic hosts as                   described in materials and methods. Numbers of surviving animals               were quantitated every two days. All values represent the                      average of two experiments each containing groups of 10-15 mice.                        Tripeptide                                                                             Treatment Period (min)                                        Tumor Cell (ug/ml)   15     30   60   120   240                                ______________________________________                                         L-1210     0         10     10   10   10    --                                 Leukemia   1         10     10   11   13    --                                            5         13      21*  32* .sup. NT.sup.1                                                                       --                                            10         8     NT   NT   NT    --                                            25        NT     NT   NT   NT    --                                 MJY-alpha  0         --     42   42   42    --                                 Mammary Tumor                                                                             5         --     --    52* 43    --                                            10        --     44   46    61*  --                                            25        --      56* NT   NT    --                                            50        --     NT   NT   NT    --                                 B-16       0         --     28   28   28    28                                 Melanoma   5         --     --   31    33*  41*                                           10        --      35*  35*  35*  45*                                           25        --      52*  68*  65*  NT                                            50        --     NT   NT   NT    NT                                 ______________________________________                                          .sup.1 NT = No Tumor.                                                          *p 0.001                                                                 

EXPERIMENTAL EXAMPLE 9 Bioassay of Tumorigenicity

Suspensions of untreated and tripeptide treated MJY-alpha mammary tumor, B-16 melanoma, and L-1210 leukemia cells were adjusted to a concentration of 1×10⁷ cells/ml based on the initial tumor cell concentration before the tripeptide exposure. Tumor cells were inoculated into syngeneic hosts at a concentration of 1×10⁶ cells in 0.1 ml. Female BALB/c/Crgl recipients of MJY-alpha mammary tumor cells and male C57BL/6/Jx hosts receiving B16 melanoma cells were inoculated subcutaneously; BDf₁ mice were given intraperitoneal injections of L-1210 cells. Subcutaneous tumors were measured along their long and short axes every 1 to 3 days; tumor size is reported as the product of the two measurements (mm²). See FIG. 8. The examination periods for mice receiving L-1210, MJY-alpha and B-16 tumor grafts were 45, 80, and 85 days, respectively. All mice were autopsied at the time of death or sacrifice.

Assessment of the tumor growth rates of the subcutaneously implanted MJY-alpha mammary tumor and B-16 melanoma cells revealed that the initial lag period between inoculation of tumor cells and the appearance of palpable tumors lengthened in both solid tumor model systems with increasing dosages of tripeptide (FIG. 8). However, tripeptide did not alter tumor progression once the graft was established; tumor growth rates of untreated and tripeptide treated MJY-alpha and B-16 cells were identical and the maximum size of the tumor at the time of death of hosts remained unchanged. This suggested that the tripeptide did not alter the kinetics of tumor cell proliferation nor did it appear to select one subpopulation of tumor cells.

EXPERIMENTAL EXAMPLE 10 Sensitivity of Mice to the Tripeptide Compound

In order to assess whether the effective cancericidal concentrations of the tripeptide compound found in the bioassays were attainable in vivo, mice were given a single intraperitoneal inoculation of the tripeptide. Demonstrable tripeptide toxicity required administration of high concentrations of the synthetic tripeptide. All mice tolerated doses of 52.5 mg/m² (15 mg/kg) with no observable signs of discomfort or pathologies. BDF₁ males which have been previously shown to be very sensitive to alkylating agents tolerated 61.25 mg PTT.119/m² (17.5 mg/kg; LD₁₀), whereas, this dose increased to 74.6 mg/m² (21.3 mg/kg) in AKR females. The LD₅₀ of male BDf₁ mice was 81.6 Mg/m² (23.3 mg/kg) and 93.5 mg/m² (27 mg/kg) for female AKR mice.

EXPERIMENTAL EXAMPLE 11 In Vitro Survival of Tripeptide-Related Tumor Cells

The reversibility of the cancericidal activity of the tripeptide compounds on L-1210 leukemia, MJY-alpha mammary tumor and B-16 melanoma cells was also monitored in the nonhostile tissue culture environment. Cell suspensions of these tumor models were treated with tripeptide for 15 to 240 min, washed and either inoculated into mice or maintained as suspension (L-1210) or monolayer cultures (MJY-alpha and B-16). Reductions in tumor cells survival were negligible (0-6%) in all three tumor systems at initiation of in vitro cultures following treatment with 50 ug tripeptide/ml for as long as 4 hrs. However, significant decreases in cellular viabilities of L-1210 leukemia (FIG. 9), MJY-alpha mammary tumor (FIG. 10) and B-16 melanoma (FIG. 11) tumor cells were observed 24 hr following tripeptide exposure and for the next 6 days.

Longitudinal examination of the cultures demonstrated that cytolysis of the tumor cells continued days after tripeptide treatment and also revealed the repopulation of tumor cell cultures treated with low concentrations of the tripeptide. A step-wise gradation in cytolysis with increasing concentrations of tripeptide was observed in the in vitro survival curves of the three tumor cell systems. At any dose of tripeptide, tumor cell survival also decreased when the treatment periods were lengthened although the L-1210, MJY-alpha and B-16 cells were refractile to these duration-related changes at several concentrations of the tripeptide. These apparent refractory phases were observed at concentrations of 10 and 25 ug of tripeptide in MJY-alpha and B-16 cells and at 1 and 5 ug of tripeptide in L-1210 leukemia cultures.

EXPERIMENTAL EXAMPLE 12

Confluent MJY-alpha mammery tumor cell layers were treated with PTT.199 or diluent for 15 or 60 minutes, washed, and then incubated in growth medium. Representative cell layers were fixed and stained with May-Grunwald-Giemsa stain from one (1) to seven (7) days after treatment as specified. Hemicysts or domes which are usually observed in short-term cultures of murine, MMTV-induced mammary tumors are not present in MJY-alpha cultures (FIG. 12a+b). Cell layers treated with 5 and 10 ug PTT.119/ml for 15 to 60 minutes appeared unchanged. Cellular pseudopodia were withdrawn and the cytoplasm appeared condensed around the nuclei (FIG. 12c+d). The most striking feature of exposure to high concentrations of PTT.119 was the ruffling of the plasma membrane and the formation of vesicles and blebs. The first detectable change was hypertrophy of the cells which initially appeared to be primarily due to increases in nuclear size as seen by comparison of FIGS. 12a and 12c. This alteration was closely followed by visible increases in the cytosol volume or rarefaction of the cytoplasm (FIG. 12f). The degree of further pathological alterations of MJY-alpha mammary tumor cells was dependent on the dosage of PTT.119 and included lobulation and fragmentation of the nuclei, and the formation of multinuclear cells (FIG. 12f+h). The increasing presence of multinucleated cells and the decreasing numbers of viable cells in these cultures indicated that cell division was not completed. Chromosomal condensation was not inhibited in multinucleated cells or in cells with highly lobulated or fragmented nuclei (FIG. 12h). FIG. 12g shows the same degree of increasing cell problem of induced irreversible nuclear fragmentation and lobulation, multi nucleation mitotic asynchrony.

EXPERIMENTAL EXAMPLE 13

Thin sections MJY-alpha mammary tumor cells were prepared according to standard techniques for electronmicroscopy. The magnification was scaled where the bar was equal to one um. As seen in part a, the untreated cells contain budding and mature B-type mouse mammary tumor virus particles. The tumor virus particles are shown in the insert and also throughout the lower two-thirds of the photograph as rope-like sections. Section B of FIG. 13 shows untreated cells containing aggregrates of intracytoplasmic A-type MMTV particles. It should be noted that numerous microvilli are present with budding particles also in evidence. Section C of FIG. 13 shows MJY-alpha cells after treatment with 25 ug PTT.119/ml. for a two (2) hour period. After that treatment period, the layer of cells was washed and then reincubated for one (1) day prior to further processing for electronmicroscopy. Although there are some microvilli with budding particles present, the number of such particles and buds is reduced. Section D of FIG. 13 shows MJY-alpha cells after treatment with 25 ug PTT.119/ml. for two (2) hours. The layer was then similarily washed and reincubated for a two (2) days prior to further processing for electronmicroscopy. Again it can be seen that the number of microvilli has been reduced even farther than from Section C and greatly reduced from the untreated cells shown in Sections A and B. Therefore, as is shown by the contrast between Sections A and B and Sections C and D, treatment with the tripeptite leads to reduced production of the virus within the tumor cells.

EXPERIMENTAL EXAMPLE 14 L-pam Cross-Resistance Test

Three ascitic leukemia cell lines maintained in BDF₁ (BALB/c×DBA/2) mice are used in this example: L1210 leukemia and two L-phenyl-alanine mustard (L-PAM) resistant lines, L1210/L-PAM and P388/L-PAM leukemia. Leukemic cells were harvested, tested for viability, and their cultures maintained according to standard techniques.

Three in vitro culture adapted lines of L1210 leukemia, the L1210S, L1210DDP and L1210 MTX (used in Example 15) were maintained in logarithmic growth phase in Fischer's medium with 10% horse serum. The L1210DDP cells were 20-fold more resistant to cisplatin than the susceptible L121OS. Likewise, L1210 MTX were 100-times more resistant to methotrexate. The resistance exhibited by both cell lines was stable and the cells were grown in the absence of drugs.

All in vitro PTT.119 and L-PAM treatment of cells were carried out at 37° C. in the appropriate complete growth media containing 10% or 18% sera. L1210, L1210/L-PAM and P388/L-PAM cell suspensions of 1×10⁶ cells/ml were subjected to a single 15, 30 or 60 min pulse exposure to 3.75, 7.5 and 15 uM PTT.119 or L-PAM. Following treatment, media were removed by pelleting the cells at 200×g for 9 min at 5° C. Cells were then gently washed twice with fresh growth media and finally resuspended in RPMI-1630 medium with 10% FBS for in vitro cultrues.

Viability of leukemia cells was ascertained immediately following and every 24 hours after pulse exposure to PTT.119 or L-PAM. During this 7-day period culture media were changed daily by gently pelletting the cells and exchanging 70% of the spent supernatant with fresh media. The viable fraction of cells continuously exposed to drugs was determined once at the end of the 24 hour treatment period. Numbers of viable cells excluding a vital trypan blue stain were enumerated with a haemocytometer by counting all fields for every sample. The means from 20 to 40 evaluations were obtained for each time point and percent viable cells in treated cultures determined by direct comparison with parallel untreated or solvent treated cells. No significant differences were observed in the viabilities of cells treated with solvent or media with no L1210/L-PAM and P388/L-PAM and the susceptible L1210 leukemia to PTT.119 significantly reduced the fraction of surviving cells. Treatment with 3.75 uM PTT.119 for as short as 30 or 60 min reduced the percentages of viable L1210 and L1210/L-PAM cells to 40-50% and the resistant P388/L-PAM leukemia cells to 0-1% within 4 to 5 days after exposure. In contrast, 80-90% of the L1210, L1210/L-PAM and P388/L-PAM cells remained viable following either a 30 or 60 min exposure to 3.75 uM L-PAM. Both resistant lines as shown in FIG. 14 were markedly more susceptible to 7.5 uM PTT.119 than the L1210 leukemia. The increased cytotoxicity was observed when drug exposure was for either 30 or 60 min and was demonstrable throughout the 6 to 7 day period following PTT.119 treatment. By the end of the examination period the surviving fractions of L1210/L-PAM and P388/L-PAM cells were reduced to 0.8-3% and 0-0.5%, respectively, compared to the 15% for the L1210 cells.

For comparison, the three leukemia lines were treated in parallel with an equimolar dose of L-PAM. Data depicted in FIG. 14 shows that PTT.119 was always more effective. L-PAM was only able to reduce the surviving cell populations of L1210 to 60-80%, L1210/L-PAM to 3-20% and P388/L-PAM cells to 7-40%. Despite the in vivo resistance of L1210/L-PAM and P388/L-PAM tumors to L-PAM, a sizable portion of the tumor cell population is susceptible to the alkylating agent.

Increasing the dosage of PTT.119 to 15 uM resulted in further reductions in cell survivals and also increased the rate of cell cytolysis of all three leukemias as shown in FIG. 15. The most significant change was observed with the L1210 leukemia. Exposure to 15 uM PTT.119 for either 30 or 60 minutes completely eliminated the viable population within 5 days of additives, therefore, numbers of control cells are averages of the two experimental controls.

Suspensions of PTT.119 or L-PAM treated cells, and control leukemia cells were adjusted to 1×10⁷ cells/ml based on tumor cell concentrations prior to drug exposure. Syngeneic female BDF₁ (BALB/c×DBA/2)f, mice weighing 20 to 26 g received intraperitoneal injections of 1×10⁶ cells. Mice were monitored daily throughout the 45 day examination period and were autopsied at the time of death.

Long-term cultures of L1210 leukemia and MJY-alpha mammary tumor cells were continuously exposed to low doses of PTT.119 by addition of the tripeptide at the time of media replacement. L1210 cells were passaged at 1×10⁵ cells/ml every 3 to 14 days and received 15 to 750 uM PTT.119 at the time of seeding.

MJY-alpha mammary tumor cells were treated with 0.15 to 15 uM PTT.119 at the time of seeding and daily, thereafter, when the medium was changed. The monolayer cultures were passaged every 7 to 21 days. L1210 and MJY-alpha mammary tumor cells exposed to low doses of PTT.119 were periodically tested for susceptibility to 1.5 to 75 uM tripeptide. L1210 cell suspensions were treated for 24 hours as previously described and viable cells enumerated using trypan blue. MJY-alpha cells from treated cultures and parallel untreated controls were seeded at 2×10⁵ cells/2 cm² while using media containing the appropriate low concentration of PTT.119. One day after plating the confluent layers were treated with additional levels of tripeptide for 24 hours. Cell layers were then released from the substrate with 0.5 ml saline-trypsin-versene, and diluted 2- to 10-fold with trypan blue prior to counting.

Exposure of primary cultures of two L-PAM resistant lines, treatment. Doubling the concentration of L-PAM increased its activity against the leukemia cells particularly when treatment was carried out for 60 minutes although L-PAM still could not eliminate all viable cells.

The tumorigenicity of the L1210 and L1210/L-PAM leukemia cells following in vitro treatment with PTT.119 was determined using syngeneic BDF₁ recipients. Mice free of tumor were present in every treatment group of both leukemias as shown in FIG. 16 and significant increases in the mean survival time (MST) were also observed in recipients which did succumb to L1210 or L1210/L-PAM tumors as detailed in Table 6.

                  TABLE 6                                                          ______________________________________                                         MEAN SURVIVAL TIME (MST)                                                       OF BDF.sub.1 MICE RECEIVING LEUKEMIA                                           CELLS TREATED WITH PTT.119 OR L-PAM                                            Tumor cells (1 × 10 6/ml) were treated in vitro, washed and              implanted into syngeneic hosts. Numbers of surviving animals                   were determined daily. All values are MST of animals who died                  of tumor and represent the average of two experiments each                     containing groups of 10-15 mice.                                                              MST in Days                                                                    TREATMENT PERIOD (min)                                          Tumor Cell                                                                               Drug/(uM)  15       30      60                                       ______________________________________                                         L1210     0              10     10      10                                               7.5   PTT.119  --     21.sup.t **                                                                            32.sup.t **                                      15    PTT.119   8.sup.t                                                                              TF      TF                                     L1210/L-PAM                                                                              0              13     13      13                                               7.5   PTT.119  --     19.sup.t **                                                                            TF                                               15    PTT.119  16.sup.t *                                                                            18.sup.t *                                                                             TF                                               7.5   L-PAM    --     15      15.sup.t                                         15    L-PAM    14     16      TF                                     ______________________________________                                          .sup.t Group also contained tumorfree animals                                  .sup.b Tumor Free                                                              *p < 0.01                                                                      **p < 0.001                                                              

PTT.119 at 7.5 and 15 uM was highly effective against L1210 cells. Approximately 80-100% of the mice in every group was free of tumor at the end of the 45-day examination period. The reduction of tumorigenicity of L1210/L-PAM cells increased as the concentration of PTT.119 and the duration of exposure increased. Complete abrogation of L1210/L-PAM tumors was obtained by treatment for 60 minutes with either 7.5 or 15 uM of tripeptide. These results indicate that PTT.119 effectively reduced the population of treated leukemia cells capable of proliferation in the tumor-free mice to 0 since the L.D.₁₀₀ is a single cell. In comparison, in vitro treatment of L1210/L-PAM leukemia with L-PAM resulted in diminution of tumorigenicity only when the cells were treated with 15 uM L-PAM for 60 min. All mice receiving cells treated with either dose of L-PAM for 15 or 30 min died of tumor (FIG. 16) with no observable increase in their MST (Table 6).

Treatment of the L-Pam resistant L1210/L-PAM and P388/L-PAM luekemias with increasing doses of PTT.119 for 24 hours revealed that these two tumor lines were more susceptible to the tripeptide than the L1210 leukemia as shown in FIG. 17. As summarized in Table 7, PTT.119 levels which decreased resistant cell survival by 50% (T.C.D.₅₀) or totally eliminated viable cells (T.C.D.₁₀₀) were markedly lower compared to those for L1210 cells.

                  TABLE 7                                                          ______________________________________                                         CYTOLYTIC EFFICACY OF PTT.119 AND L-PAM                                        L1210, L1210/L-PAM and P388/L-PAM cell suspensions (1 × 10.sup.6         cells/ml) were treated for 24 hours and the percentage of viable               cells compared to untreated cells and control cells receiving                  diluent. T.C.D..sub.50 and T.C.D..sub.100 values represent the means of        25-40 determinations. Viabilities of untreated and solvent                     treated tumor cells were 98-100%                                                        T.C.D..sub.50 (uM)                                                                          T.C.D..sub.100 (uM)                                      Cell Line  PTT.119  L-PAM     PTT.119                                                                               L-PAM                                     ______________________________________                                         L1210      9.0      22.5      37.5    75.0.sup.§                          L1210/L-PAM                                                                               3.0       3.8      30.0   163.0.sup.§                          P388/L-PAM 5.0      11.0      22.5   163.0.sup.§                          ______________________________________                                          .sup.§ Cultures contained 0.2-3% viable cells at 24 hours.          

Parallel treatment of the three tumor cell lines with L-PAM demonstrated significant differences between the efficacies of PTT.119 and L-PAM FIG. 17. The cytolytic activity of PTT.119 was always greater than equimolar concentrations of L-PAM. In addition to this quantitative difference, a plateau was observed in the dose response curves the of L1210/L-PAM and P388/L-PAM leukemia treated with L-PAM. A residual number of cells in each of the leukemia populations was unaffected by increasing the L-PAM concentration in excess of 30 uM. As a result the survival of these L-PAM resistant lines could not be completely abrogated and at 163 uM L-PAM approximately 0.2% of the L1210/L-PAM and 3% of the P388/L-PAM populations remained viable (Table 7). The results show that these tumor cell lines maintained in mice are a heterogeneous mixture of both L-PAM susceptible and resistant cells. However, the complete cytolysis of all L1210/L-PAM and P388/L-PAM cells by PTT.119 at concentration similar to the susceptible L1210 leukemia demonstrates the lack of any detectable cross-resistance to the tripeptide.

EXPERIMENTAL EXAMPLE 15 MTX and Cisplatin Cross-Resistance Test

The cytolytic efficacy of PTT.119 against leukemic cell lines made resistant to the 2,4 diaminofolate antagonist methotrexate (L1210 MTX; T.C.D.₅₀ 0.5 uM MTX) and the alkylating agent cis-diamminedichloroplatinum (II) (L1210DDP; T.C.D.₅₀ 30 uM cisplatin) was examined and compared to the parental L1210S (T.C.D.₅₀ is 5 nM for MTX and 1.5 uM for cisplatin). Methods for harvesting, testing, and maintaining cultures were performed in the same manner used in Example 14.

As shown in FIG. 18 the viability of both resistant lines were decreased in a dose dependent manner following 24 hours exposure to the tripeptide. The L1210 MTX line was more susceptible in comparison to the L1210S leukemia; the T.C.D.₅₀ and T.C.D.₁₀₀ of L1210 MTX were 1.94 uM and 3.75 uM, respectively, compared to 2.38 uM (T.C.D.₅₀) and 7.5 uM (T.C.D.₁₀₀) for the L1210S. The L1210DDP line was also completely susceptible to PTT.119 although the dose response curve indicates the existence of at least two subpopulations of leukemic cells with varying sensitivities to the tripeptide. Approximately 60% of the L1210DDP leukemic cells were highly susceptible to PTT.119 doses of 1 uM (T.C.D.₅₀ 0.525 uM) with the remaining population becoming sensitive to the tripeptide at 4-15 uM. The small plateau in cell viability was consistently observed in every trial with the tripeptide. The data suggests that the cloned population of L1210DDP which displays a homogeneous response to cisplatin treatment is heterogeneous with respect to its sensitivities to another alkylating agent.

EXPERIMENTAL EXAMPLE 16 PTT.119 Induced Resistance Test

The ability of PTT.119 to induce drug resistant cells was examined by maintining tumor cell lines in the presence of low concentrations of the tripeptide. The first series of these experiments involved continuous treatment of the susceptible MJY-alpha cells (T.C.D.₅₀ 1.5, 7.5 or 15 uM PTT.119). Monolayers grown in the presence of 15 uM PTT.119 did not survive beyond the second passage. MJY-alpha cells exposed to the three lower concentrations of PTT.119 were successfully maintained for 8 months. The growth rates of these treated cells (alpha-0.15, alpha-1.5, alpha-7.5) were diminished resulting in their subculture every 1.5-2 weeks compared to the weekly passage of the untreated parental cells. The susceptibility of alpha-0.15, alpha-1.5 and alpha-7.5 to PTT.119 was tested periodically by 24 h exposure to six concentrations of the tripeptide (1.5, 3.75, 7.5, 15, 37.5 and 75 uM). No alteration in the dose response curves of the three PTT.119-treated lines were observed compared to previously untreated MJY-alpha cells.

Long-term in vitro suspension cultures of L1210 leukemia cells have also been continuously treated with PTT.119 at 15, 75, 150, and 1500 nM. Cells treated with tripeptide doses of 75 nM or greater were all rendered nonviable within the first 3 or 4 subcultures. Two cell lines L1210-T1 and L1210-T2 were maintained in 15 nM PTT.119 for 28 and 23 passages, respectively. The dose responses of L1210-T1 and L1210-T2 cells at 24 hours PTT.119 treatment was repetitively tested. An increase in resistance to PTT.119 at the concentrations of 15 and 22.5 uM was observed in both lines between the 8th and 16th passages. At these two doses, PTT.119 cytotoxicity was found to be 20-30% lower compared to untreated L1210 cells. However, resistance was not stable and by the 20th passage no differences could be detected in the dose response curves of L1210, L1210-T1 and L1210-T2.

Further attempts to induce an L1210 line resistant to PTT.119 by escalation of tripeptide dosage were caried out. At the 29th passage of L1210-T1, the concentration of PTT.119 was increased to 37.5 nM. Characterization of the dose response of L1210-T1 maintained at this higher concentration for 25 passages has demonstrated that thus far no resistant L1210 cells have been induced by the tripeptide. Further escalation of the tripeptide concentration to 52.5 nM rendered the L1210-T1 cells nonviable within 6 subcultures. These studies using the L1210 leukemia and the MJY-alpha mammary tumor cell line demonstrate that resistance to PTT.119 is very difficult to induce and strongly indicates that inclusion of carrier amino acids in the parental bis-(2-chloroethyl)amino bifunctional alkylating moiety renders the tripeptide an extremely poor mutagen.

We hypothesize that the observed increase in PTT.119 cancericidal activity is related to the structural alteration of the parental m.L.SL molecule which contains the bis-(2-chloroethyl)amino bifunctional akylaing moiety. The evidence suggests that linkage of phe and met in the L configuration to the amino- and carboxyl-groups of the phe residue of m.L.SL alters and/or increases the transport of PTT.119 across the tumor cell membrane. This change in PTT.119 transport could account for the increased cytolytic efficacy of the tripeptide compared to m.L.SL or its structural isomer L-PAM observed in this investigation. 

What is claimed is:
 1. The method of treating tumor cells comprising:culturing the tumor cells with L-PAM, methotrexate, or cisplatin whereby the tumor cells become resistant to L-PAM, methotrexate, or cisplatin; administering to the tumor cells in vitro at a therapeutically effective dose for treating tumor cells a tripeptide compound, selected from the group consisting of:(a) 3-(p-fluorophenyl)-L-alanyl-3-[m-bis(2-chloroethyl)-aminophenyl]-L-alanyl-L-methionine (b) 3-[m-bis(2-chloroethyl)aminophenyl]-L-alanyl-3-(p-fluorophenyl)-L-alanyl-L-methionine (c) 3-(p-fluoropheny)-L-alanyl-L-methionyl-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanine (d) 3-[m-bis(2-chloroethyl)aminophenyl]-L-alanyl-L-methionyl-3-(p-fluorophenyl)-L-alanine (e) L-methionyl-3-(p-fluorophenyl)-L-alanyl-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanine (f) L-methionyl-3[m-bis(2-chloroethyl)aminophenyl]-L-alanyl-3-(p-fluorophenyl)-L-alanine.
 2. The method of claim 1, wherein the tripeptide compound is 3-(p-fluorophenyl)-L-alanyl-3-[m-bis(2-chloroethyl)aminophenyl]-L-alanyl-L-methionine ethyl ester hydrochloride.
 3. The method of claim 2, wherein 10 mg of the tripeptide is first dissolved in a solution of 0.25 ml of N-N-dimethylacetamide, 0.25 ml of absolute ethanol and 0.5 ml of propylene glycol; preparing a stock solution by further diluting the dissolved drug in an aqueous solution of 50% propylene glycol to a concentration of 1 to 2 mg per ml; and administering the tripeptide compound at concentrations ranging from 0.5 to 50 ug per ml of the tumor cells for 15 minutes to 24 hours at 37° C.
 4. The method of claim 2, wherein 10 mg of the tripeptide is first dissolved in a solution of 0.25 ml of N,N-dimethylacetamide, 0.25 ml of pure ethanol, and 0.5 ml of propylene glycol; preparing the solution by further diluting the dissolved drug in an aqueous solution of 50% propylene glycol so that the stock solutions are concentrated in a range of 1 to 2 mg per ml; exposing the tumor cells to 0.5 to 50 ug of the tripeptide compound per ml of solvent for pulse exposure from 0.25 to 4 hours.
 5. The method of claim 2, wherein the tumor cells are a member selected from a group consisting of MJY-alpha murine mammary cells and B-16 melanoma cells.
 6. The method of claim 5, wherein the tumor cells are in a layer density of approximately 2×10⁵ cells per sq. cm. of well.
 7. The method of claim 2, wherein the tumor cells are a member selected from the group consisting of murine L-1210 leukemia cells and primary human leukemia cells.
 8. The method of claim 7, wherein the tumor cells are at cell concentrations of 6-10×10⁵ cells/ml.
 9. A method of treating tumor cells resistant to L-PAM, methotrexate or cisplatin comprising:(a) preparing a therapeutic quantity of a tripeptide compound in a pharmaceutical vehicle, said tripeptide compound being 3-(p-fluorophenyl)-L-alanyl-3-[m-bis-(2-chloroethyl)aminophenyl]-L-alanyl-L-methionine ethyl ester hydrochloride; (b) administering in a repetitive dosing regimen said pharmaceutical vehicle containing said tripeptide compound to a malignant tissue containing said resistant tumor cells.
 10. The method of claim 9, wherein said therapeutic amount is between about 3.75 uM to about 15 uM for an exposure time of between about 15 minutes to about 60 minutes.
 11. The method of claim 10, wherein said repetative dosing regimen for administering said therapeutic amount of said tripeptide compound for said exposure time is about a 24 hour period.
 12. The method of claim 9, wherein said malignant tissue is treated in an in vitro condition.
 13. The method of claim 9, wherein said malignant tissue is treated in an in vivo condition.
 14. The method of claim 9 wherein said resistant tumor cells are a member selected from the group consisting of murine L1210 leukemia cells and primary human leukemia cells.
 15. The method of claim 9, wherein said resistant tumor cells are primary human leukemias.
 16. The method of claim 7, wherein said primary human leukemia is a member selected from the group consisting of human AMML leukemia, human ALL leukemia, and hairy cell leukemia. 